Productivity of mixed plantations of ash and larch in northeastern China – a model-based analysis

Abstract

Mixed forests are favored in forest management because of their higher biodiversity and resilience than pure stands. The productivity of a mixed stand may be better than the average of monospecific stands of those species that form the mixed stand. In northeastern China, most plantation forests are monocultures, but mixed plantations are also increasingly established. Several experiments of planted mixtures of Changbai larch (Larix olgensis) and Manchurian ash (Fraxinus mandshurica) have been established in the Heilongjiang province of northeastern China. This study analyzed the growth and mortality of the trees in these experiments at ages 15–30 years. Both distance-dependent and distance-independent tree-level models for diameter increment and mortality were developed. The analyses showed that competition indices calculated from tree heights performed better than indices based on trunk diameters, indicating the importance of competition for light. The models suggested that ash benefits from a larch admixture, but larch does not benefit from the presence of ashes. Simulations conducted using the models showed that, at stand ages of 15–30 years, ash stands were more productive than mixed or pure larch stands. Because the two species performed differently in different experiments and plots, no overall conclusions could be drawn about the overyielding or under-yielding of mixed stands. In some sites, the mixture may be more productive than the average of pure stands, but this conclusion cannot be generalized.